Physicians have long assumed that early follow-up scans for residual or recurrent thyroid cancer are only possible when patients have been through six weeks of a weaker thyroid medication and two to three weeks of no thyroid medication.
Withdrawal from medication leads patients' bodies to produce their own thyroid-stimulating hormone (TSH), and exposure to sufficiently high levels of TSH creates an increased thirst for iodine in any remaining thyroid cells. Scientists can then give patients small doses of radioactive iodine that will be taken up by the cells. A weaker dose lets scientists detect the cells; a stronger dose kills them.
In a study published in the April issue of The Journal of Nuclear Medicine, Washington University School of Medicine scientists report that simply taking patients off thyroid medication for two weeks prior to the scan produces the desired changes in nearly 90 percent of patients.
"When patients are taken off thyroid medication, they get tired, gain weight and just generally don't feel very good," says lead investigator Perry W. Grigsby, M.D., professor of radiology and of radiation oncology. "We don't want patients to feel bad, so we want them to be off medication for as short a time as possible."
Physicians diagnose an estimated 14,000 new cases of thyroid cancer per year, with women developing the cancer at rates two to three times those of men. Located in the neck, the thyroid gland regulates metabolism through the production of thyroid hormone, which affects cell activity levels throughout the body.
Treatment of a cancerous thyroid generally begins with surgical removal of the gland. To compensate, patients take thyroid medication for the rest of their lives.
In early postoperative scans, increased risk of recurrent or residual tumors limits physicians' options for preparing patients for those scans, according to Grigsby.
"The classic procedure is to put the patient on a weaker thyroid medication for six weeks and then take them off medication entirely for two to three weeks," Grigsby explains.
For the study, Grigsby and colleagues closely monitored the TSH levels in nearly 300 thyroid cancer patients whose thyroids had been removed and who were not taking medication. Some of the patients were just out of surgery and hadn't yet started taking the hormone; others were taken off the hormone without the standard six-week period on the weaker form of the drug. Researchers found that 89 percent of the group had achieved the TSH level needed for postoperative imaging in one to two weeks. By the third week, 96 percent were at or beyond the desired level.
"We don't seem to need six weeks on the less effective medication," Grigsby says. "That approach appears to have originated as someone's best guess as to what we needed to do to prepare patients for scans, and no one ever questioned it. But now we know we can do it in a way that is simpler, quicker and above all easier on patients."
Grigsby notes that the introduction of recombinant human thyroid-stimulating hormone (rhTSH) five years ago greatly reduced the need to take patients off thyroid medication for later follow-up scans. The body responds to rhTSH in the same way it responds to cessation of thyroid medication, making it possible for scientists to scan for cancer cells.
However, rhTSH can also complicate and delay treatment of tumors, so physicians generally do not use it in the earliest postoperative scans, when odds of finding tumors again are highest.
Grigsby PW, Siegel BA, Bekker S, Clutter WE, Moley JF. Preparation of Patients with Thyroid Cancer for 131I Scintigraphy or Therapy by 1-3 Weeks of Thyroxine Discontinuation. Journal of Nuclear Medicine, April 2004.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient-care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.
Journal
Journal of Nuclear Medicine